Chapter 2: Polar Covalent Bonds and Acids/Bases

the two acid/base definitions

- Bronsted and Lowry - Lewis Acids and Bases

types of organic acids

- H bonded to electronegative O atom - H bonded to C that's next to a C=O

acidity constant

- Ka - a measure of acid strength

polar covalent bonds

- a covalent bond in which the electron distribution between atoms is uneven - the in-between step from covalent to ionic

resonance hybrid

- a molecule that can't be represented adequately by a single kekule structure but must be considered as an average of two or more resonance forms

Bronsted-Lowry base

- a substance that accepts a hydrogen ion from an acid

Bronsted-Lowry acid

- a substance that donates a hydrogen ion to a base

Lewis base

- a substance that donates an electron lone pair to an acid - includes all nucleophiles - can be most O and N containing compounds

Lewis acid

- a substance with a vacant low-energy orbital that can accept an electron pair from a base - includes all electrophiles - lots of metal cations, compounds of group 3A elements, and multiple transition metals

resonance forms

- an individual structural form of a resonance hybrid - only difference between forms is in placement of bonds and nonbonding electrons

dispersion forces

- between all neighboring molecules - temporary bonds on small scale that happen so rapidly that it permenatly keeps molecules together

dipole-dipole interactions

- between polar molecules - can be attractive or repulsive

types of non-covalent interactions

- dipole-dipole - dispersion - hydrogen bonds

strong acids

- fully (almost fully) dissociate in water - have large Ka and small pKa

radicals

- have 1 electron (not lone pair) - depict movement with half-curved arrow

organic bases

- have atom with lone pair of electrons that can bond with H ion - most commonly are compounds with N and/or O

rules for resonance forms

- individual resonance forms aren't real - forms only differ in placement of pi-bonds and nonbonding electrons - different forms of substance aren't always equivalent - forms must obey octet rule - hybrid more stable that any individual form

non-covalent interactions

- one of a variety of nonbonding interactions between molecules

super molecular chemistry

- study of systems involving aggregates of molecular ions held together by non-covalent interactions

electronegativity

- the ability of an atom to attract electron in a covalent bond - increases across the periodic table from right to left, and bottom to top - causes polarity of molecule

inductive effect

- the electron-attracting (or electron withdrawing) effect transmitted through sigma bonds - electronegative elements have electron-withdrawing inductive effect

conjugate base

- the product that results from deprotonation of a Bronsted-Lowry acid - Strong acid has a weak conjugate base

conjugate acid

- the product that results from the protonation of a Bronsted-Lowry base - Strong base has a weak conjugate acid

dipole moments

- used to measure net molecular polarity - occurs when the centers of mass of positive and negative charges within a molecule don't cancel out.

hydrogen bonds

- very strong dipole-dipole interaction - major affect on natural processes - a weak attraction between hydrogen atom bonded to an electronegative atom and an e-lone pair on other electronegative atom

List of specific lewis acids

-TiCl4 -FeCl3 -ZnCl2 -SnCl4 -AlCl3

hydrophilic

-readily dissolves in water

formal charge

-the difference in the number of electrons owned by an atom in a molecule and by the same atom in its elemental (atomic) state - closely related to electronegativity and dipole moment - way to track "ownership" of electrons

carbon's electronegativity

2.5

1 Debyes = ?

3.336 x 10^-30 C*m

acidity constant equation

= [(concentration of Hydronium ions) X (concentration of conjugate base)]/ (concentration of acid)

formal charge equation

FC = (# of valence electrons in free atom) - (# electrons in bonded atom) OR FC = (# of valence electrons in free atom) - (# of bonding electrons/2) - (number of nonbonding electrons)

hydrophobic

does not readily dissolve in water

ionic bond electronegativity

greater than 2

nonpolar-covalent bond electronegativity

less than 0.5

the conjugate acid of a weak base

strong acid

the conjugate base of a weak acid

strong base

pKa

the negative common log of Ka - used to express acid strength

the conjugate acid of a strong base

weak acid

the conjugate base of a strong acid

weak base

dipole moment equation

DM (dipole moment) = Q x r (Q = charge at either end of molecule dipole, r = distance between charges)

important example of organic bases

amino acids

polar-covalent bond electronegativity

between 0.5 and 2.0